COMBUSTION PROCESSES are extremely difficult to characterize in terms of the chemical processes occurring. This is in part the result of high temperatures and the use of complex fuels. The resultant combustion streams are composed of a variety of species which include radicals, ions, stable molecules, and condensed matter such as soot and fly ash. This complex environment leads to a myriad of homogeneous reactions as well as heterogeneous reactions occurring at the surface of entrained particles. The heterogeneous reactions are further complicated by the presence of trace metals and clay materials which can act as catalysts.

Coherent anti-Stokes Raman spectroscopy (CARS) appears very promising for the remote, spatially and temporally precise probing of hostile combustion environments due to its large signal conversion efficiency and coherent signal nature. CARS is a wave mixing process in which incident laser beams at frequencies w1 and 0)2, with a frequency difference tuned to a Raman resonance in the molecular species being probed, interact to generate a coher-ent signal at frequency w3 = 2(.01 - w2. By analyzing the spectral distribution of the CARS signal, temperature measurements can be performed. Species concentration measurements derive from the intensity of the CARS radiation or, in certain cases, from its spectral shape. CARS spectra have been recorded in a variety of flames from the major flame constituents and generally show very good agreement with computer synthesized spectra. Significantly, CARS has been successfully demonstrated with both liquid and gaseous fuels in the primary zone and exhaust of practical combustors. Both thermometry and species concentration measurements have been performed. High pressure effects on CARS spectra have also been examined.

The present ability of atomic and molecular fluorescence techniques to monitor quantitatively the concentrations of species in flames is reviewed. Atomic fluorescence measurements require a saturation mode with a laser pulselength that is sufficiently short to avoid induced chemical or ionization effects but long enough to produce a steady state distribution over the accessible energy levels. Molecular fluorescence techniques are available for both low laser power and saturated modes of operation and invariably involve some level of approximation due to the complex energy level manifold that is involved. Two-photon induced fluorescence detection of atoms and molecules is of potential interest in facilitating the monitoring of various additional species that previously was only possible spectroscopically in the vacuum ultraviolet. Results of the major applications of these techniques are presented. These include temperature measurements, studies of the SOX and NOx flame chemistries, methods of obtaining energy transfer rates, laser induced chemical kinetic data, and their potential for deriving thermochemical values.

Abstract. Laser-induced fluorescence (LIF) is a method of considerable utility for the measurement of the transient free radicals which are the keys to the chemistry of flames. Collisions experienced by the electronically excited state can alter the magnitude and the spectral form of the fluorescence signals. Recent studies on both quenching and energy transfer collisions, and their influence on LIF measurements, are treated in this review; special emphasis is given to the important and popular OH molecule. Different solutions to the problem of accounting for quenching are considered, and both effects and exploitation of energy transfer within the excited state are discussed. Although further research is needed to better quantify these collisional effects, LIF can currently provide data significant for the understanding of combustion chemistry.

This paper reviews the application of optogalvanic spectroscopy to flames. Optogalvanic spectroscopy is a method of obtaining absorption spectra of atomic and molecular species in flames and electrical discharges by measuring voltage and current changes upon laser irradiation. The technique alleviates problems associated with optically monitoring either small absorptions or weak fluorescence in the presence of strong laser light. Optogalvanic spectroscopy in discharges has been useful in characterizing laser linewidths as well as provid-ing a convenient frequency calibration for tunable dye lasers. In addition, opto-galvanic signals have been used to frequency stabilize continuous-wave dye lasers. Optogalvanic spectroscopy has also been possible on some molecular species which exist only in flame or discharge environments. Analytical flame spectrometry utilizing the optogalvanic effect for trace metal detection shows significant promise for many metallic elements. The optogalvanic effect can also serve as a probe of ionization effects in flames. Ionization cross sections and ion mobilities may be determined from an analysis of optogalvanic signals. This technique has been extended to include determination of mobilities for soot precursor species. Flow velocities may also be determined in laminar flames by following the residual depletion of neutrals due to laser-enhanced ionization.

Optical methods for particle size distribution measurements in practical high temperature environments are approaching feasibility and offer significant advantages over conventional sampling methods. The present paper begins by summarizing user requirements for research and on-line particle measurements in fossil fuel systems. The principles of single particle counter (SPC) design are outlined followed by a discussion of practical instrument design constraints. Three instrument design concepts currently being developed at Sandia are then discussed. An overview of these current methods and other instrument designs is presented with particular emphasis on capabilities to meet user ojectives. Validation and long term testing of these new concepts is considered to be the final important step in achieving user acceptance of in situ optical counters.

The increased use of dirty fuels such as coal and oil shale in station-ary combustors has increased the necessity for controlling NOx emissions. A potential method to accomplish this goal is the thermal deN0x process, where ammonia added to the combustion exhaust gas chemically converts nitric oxide to harmless products (N2 and H20). A complete understanding of the chemical processes occurring has been hampered by a lack of detailed high-temperature kinetic data. Using a high-temperature fast flow reactor equipped with a variety of optical detection devices, key rate parameters and product channels are determined for this process, and, in conjunction with computer modeling, a consistent comprehensive model is developed which describes the features of the NHi/NOx chemical system.

There is considerable interest in the need to improve the operation of systems which can potentially serve as alternate energy sources. Entailed in this effort is the desire to understand the vapor phase chemistry and compounds which may enter as by-products of the system under consideration. These compounds may have deleterious effects on the gas phase chemistry or play an important role through high temperature gas-solid corrosion kinetics. Here we outline the nature of the problem and focus on a subset of these molecules, the metal hydroxides and the alkali oxides and sulfides. A critical analysis of the data base is presented and new experiments are outlined which encompass the investigation of thermochemistry and the evaluation of molecular parameters through the study of visible, infrared, microwave and electron spin resonance (ESR) spectroscopy. Recent chemiluminescent experiments which lead to the evaluation of a new stringent lower bound for the K-OH band energy are summarized. This stringent lower bound (88.2 kcal/mole) correlates within the quoted error bounds with the absolute upper bound of previous experimental determinations. Preliminary laser fluorescence studies on Na20 are reported and the possible influence of "ultrafast" energy transfer (E-E and V-E transfer among the excited states of high temperature molecules) on the behavior of energy generating systems is noted.

A time-integrating optical processor is configured for one-dimensional chirp correlation spectrum analysis. A unique optical implementa-tion, utilizing Te02 shear wave acousto-optic cells, is designed to operate in a configuration which allows wide bandwidth diffraction to both the positive and negative first diffraction orders. The result is high optical throughput efficiency, excellent fringe visibility, and a coaxial system design. Chirp linearity experiments confirm coherence requirements for chirp transform processors.

The radiographic grid is an array of high atomic number blades interleaved with relatively transparent ones. The radiograph of a grid is a grating having a square wave transmittance function. If two such radiographs are superposed in a convenient way and looked at on a film viewer, moire fringes appear. From visual inspection of the fringes several structural defects in the grid show up. Some pictures explain how to enhance line defects, frequency, and pulse width modulation defects, all of them being related to uneven thickness of the blades which form the grid. Other manufacturing defects, which do not affect the periodical structure and must therefore be detected by other test methods, are also discussed.

Noncoherent-optics systems are linear in irradiance, which is a nonnegative, real quantity; bipolar and complex data must be indirectly represented. We compare spatial representation methods and evaluate their relative merits.

The advent of mosaic focal planes, with their accompanying complexity, demands a clear delineation and a wide perspective of architectural levels for the optimum design and integration of focal planes. This overview describes the important characteristics of the various architectural levels, pinpoints the main constraints on focal plane architecture, and highlights the major issues and trends in focal plane technology.

The research reported here was initially stimulated by a contradiction in the literature that suggested there was no significant performance advantage for manipulator operators employing stereo versus conventional TV systems, while typical direct-viewed results indicated that binocular performance is always superior to monocular performance in tasks requiring depth judgement or distance estimation. This paper presents an analysis of the interaction of several important variables involved in visual display research, with particular reference to our own research comparing mono and stereo TV displays in simulated underwater environments. Three experiments were conducted in our lab to assess the impact of degraded visibility on remote manipulator operator performance using either mono or stereo TV. Subjects were required to perform tasks which differed markedly in the number and type of depth cues available. As predicted, the results indicated that stereo performance was superior to mono under most conditions tested; however, the amount of improvement was shown to be a complex function of visibility, task, and learning factors. Conclusions and recommendations for further research aimed at understanding the relative contributions of these and additional display factors are presented for discussion.

The principles of limited-angle reconstruction of space-limited objects using the concepts of "allowed cone" and "missing cone" in Fourier space are discussed. The distortion of a point source resulting from setting the Fourier components in the missing cone to zero has been calculated mathematically, and its bearing on the convergence of an iteration scheme involving Fourier transforms has been analyzed in detail. It was found that the convergence rate is fairly insensitive to the position of the point source within the boundary of the object, apart from an edge effect which tends to enhance some parts of the boundary in reconstructing the object. Another iteration scheme involving Radon transforms was introduced and compared to the Fourier transform method in such areas as root mean square error, stability with respect to noise, and computer reconstruction time.

Since images in conventional radiographic tomography are in-herently low in subject contrast, it is essential that scattered radiation be prevented from reaching the image receptor. Scanning beam or slit radiographic techniques are known to be the most efficient scatter elimination methods, yet have been inapplicable to this area of radiography. In this work it is shown that the scanning beam method using rotating aperture wheel (RAW) devices can be used in conventional tomography. One coder wheel between the x-ray tube and patient and two scatter discriminator wheels between the patient and image recep-tor form sections of the RAW "projection cone" with the lines of radia-tion from the x-ray source forming the "flux pyramid." As long as the projection cone follows the motion of the x-ray flux pyramid (with the ratios of the distances between the x-ray source, RAWs, patient, and image receptor kept constant throughout the motion) any RAW pattern may be used. Simple relations are given which describe the geometric constraints for various tomographic motions. As in any application of scanning slit techniques, it is possible to use the excellent scatter elimination capabilities of a RAW device either to improve image contrast or to reduce patient dose.

The complex spectrogram of a signal is defined as the Fourier transform of the product of the signal and the shifted and complex conjugated version of a so-called window function; it is thus a function of time and frequency, simultaneously, from which the signal can be reconstructed uniquely. It is shown that the complex spectrogram is completely determined by its values on the points of a certain time-frequency lattice. This lattice is exactly the one suggested by Gabor in 1946; it arose in connection with Gabor's sugges-tion to expand a signal into a discrete set of Gaussian elementary signals. Such an expansion is a special case of the more general expansion of a signal into a discrete set of properly shifted and modulated window functions. It is shown that this expansion exists. Furthermore, a set of functions is constructed, which is bi-orthonormal to the set of shifted and modulated window functions. With the help of this bi-orthonormal set of functions, the expansion coefficients can be determined easily.

A giant pulse laser Raman probe suitable for gas concentration detection below 100 ppm with high local (0.6 mm3) and temporal (pulse width 20 ns) resolution is presented. Concentration values of some selected gaseous pollutants have been detected in pure gases and in adjusted gas mixtures ranging from the pure component (106 um) down to measured 65 um. For test conditions under atmospheric pressure and ambient temperature concentration, values of 100 ppm were measured with an accuracy of ± 100%. When the local resolution was not required to be so high-measurement volume about 500 mm3-concentration values of 65 ppm could be detected with an accuracy of about ± 30%.

Abstract. A new type of low power magnifier has been designed and fabricated. In addition to the magnification, the line of sight is deflected, which is con-venient under certain circumstances. Several applications for this type of magnifier are proposed.

Various methods for simulation of reticle systems will be described which have practical applications for the simulation of missile guidance systems. The reticle pattern, as well as the received image, is digitized using common picture processing equipment. The sampled representations of the reticle and image are converted to a polar coordinate system, and the data is then put into a vector string. Setting up a cyclic matrix with this vector string, one can describe the periodic system signal by cyclic convolution of reticle string and image string. A similarity transform to the Jordan form of a quadratic cyclic matrix, by means of the discrete Fourier matrix, reduces the amount of calculations required. This is a great advantage in digital simulation. For this linear discrete system approximation, the transfer function in the Z-domain can be deduced. This approach gives a better insight into the overall performance of the control system. The analysis also shows the limitations of reticles, which has resulted in the decline of this technique for guided missile applications.

Optical image processing has been concentrated chiefly upon processes such as image restoration and enhancement. A very fruitful area of digital image processing has been the field of image data compression. Since an earlier demonstration of the potential for optical processing in image data compression, research has been underway to extend the repertoire of image data compression methods suitable for optical processing. In this paper we describe the most recent results, a method for image data compression which concentrates its code bits in regions where image edge activity is not pronounced.

A satellite interferometer system (SIS) utilizing 1 O laser heterodyne systems has been investigated. In its simplest form, the system consists of a pair of satellites, one in a polar orbit and the other in a synchronous orbit. The spatial frequencies covered in a twelve hour observing period extend upward from the inverse of the earth's diameter, corresponding to a resolution of 10-12 radians. Absolute phase, corresponding to the constantly changing baseline between the two satellites, is measured by a simultaneous heterodyning of a calibration laser traversing the distance between the two satellites. The orienta-tion of the baselines is recorded from timing and sequencing the data, with corrections for time dilation and other perturbations.

An optical bench for developmental testing of chemical laser hard-ware is described. It is specially designed to withstand the vibration and thermal disturbances inherent in this type of laser, and has universal features which enable it to accept a variety of nozzle and mirror sizes. The paper deals with the adaptation of traditional designs to meet new requirements in the areas of bench deflection, adjustable mirror mounts, and remote mirror actuation for closed cavity power measurements. In particular, a noncantilever mount with offset pivot for heavy mirrors is described.

In a recent publication Ushioda et al. (Phys. Rev. B. 19(8) 4012 (1979)) (henceforth referred to as I) reported an experiment in which Raman excitation of surface polaritons was performed using several rough surfaces. The authors of I observed an increase, with surface roughness, of the Raman scattering intensity, but were unable to give a theoretical explanation of this surprising effect. We suggest an explanation which is based on the similarity existing between Raman excitation of surface polaritons of frequency w along a grating and grating generation of surface polaritons using an incident electromagnetic (EM) wave of the same frequency w. We determine the surface polariton wave along the grating and find a strong enhancement of its intensity when increasing the groove depth. Thus, there is a good qualita-tive agreement between our results and those published in I. This allows us to show that the phenomenon observed by the authors of I is related to the existence of Wood anomalies of gratings.

Shadowgraph and schlieren techniques have been used on board the NASA KC-1 35 low-gravity simulation aircraft to measure gravity-related fluid flow occurring in various experimental configurations. These configurations included cooled and solidified ammonium chloride and water, electrodeposited cobalt in CoSO4 solution, and immiscible and crystal melt solutions. Hardware tests have also been performed for such critical optical system components as lasers and spatial filters to determine their performance and operation under low-gravity conditions. These test results will be used in the design of the various future Shuttle experiments which will utilize advanced optical mea-surement techniques. The design and configuration of the optical systems used to make these measurements and tests are presented, and the performance and operation of these systems and their components under low-gravity conditions are discussed. Some preliminary results are included.

The approach to the design of an optical computer or processor system has typically been analog in nature in the past. Recently design concepts for a numerical optical processor have evolved in which we see digital techniques implemented with optical devices. This paper describes design concepts for a numerical optical processor which is based on the residue number system.

The technique described results in a display gamma function where the contrast between each of the steps is equally discriminable. Digital cathode ray tube (CRT) (and film) displays set up using this technique tend to have high image quality as judged by reconnaissance image interpreters. The procedure starts with a set of 51 photometric measures of a specific set of digitally-controlled targets designed to determine the interaction between the display's target and surround luminances, and the display's useful luminance range. These data are used in the Rogers-Carel formula for predicting visual threshold of within-target modulation contrast, m, as a function of target luminance, surround luminance, visual size of the target, and spatial frequency of detail within the target. Through curve fitting, optimization of viewing distances, and other operations, the equation is reduced to m = f(1), where (is the luminance when all the display pixels are commanded to the same level. This equation is used to determine the number of just noticeable differences (JNDs) within the useful display luminance range and then to determine the luminance value for each command level so that each succeeding step represents the same number of JNDs.

The current state of the art of photodetectors, both PIN and avalanche, for 1.1 to 1.6 um operation is reviewed. The devices are compared as components of optical receivers using several different types of amplifiers. GalnAsP/InP PIN and avalanche photodiode (APD) detectors are shown to be clearly superior to Ge devices with respect to dark current and other sources of noise. Receivers with performance within a few dB of the quantum limit appear to be possible with current technology.

Figure 6 should be rotated counterclockwise by 90°.

The SPIE Reports section of Optical Engineering is a vital part of the journal. I hope it serves the optics community in many ways the archival part of the journal cannot possibly serve. Appropriate goals include: technology alerts (hot new developments outlined and summarized); technology maps (who is doing what at various locations) book reviews; personal, signed opinions by qualified experts (with opposing views welcome); computer program exchanges meeting notices; new product and new literature announcements; industry news; news about people in the optics community placement exchange Perhaps you can think of more. What would you like to know? How can we serve your needs?

Improved performance in many optical instruments has been achieved by considering coherence effects in the design of the optical instrument. In this paper such improvements are reviewed by heuristically describing the fundamental principles of partial coherence which are required in the design of such instruments. Furthermore, these coherence effects, which arise from both coherent and incoherent sources of radiation, are illustrated by discussing a selected set of instruments in which improved performance has been achieved. These examples include high-resolution recording and analyz-ing instruments which use incoherent sources, as well as imaging and men-suration instruments which use coherent sources. A set of guidelines for determining when coherence effects influence system performance with re-spect to linearity, resolution, and noise is also presented.